According to Don Siegel, it was the policy at "Universal" at the time to shoot the last scene of the film first. On that first day of filming, according to Siegel and Clu Gulager, Lee Marvin arrived late and had been drinking, but because he had no dialogue, the scenes were used as shot.
NBC made a thirty-picture deal with MCA Inc. to produce "Project 120", a series of two-hour features made for TV. The first one was to be "Johnny North", a.k.a. "The Killers". It was to be the first made-for-TV movie shot in color, and it had the longest shooting schedule for such a film up to that time - four weeks. But due to the violence and sexual content, the title was changed, and it released in movie theaters.
Despite having a score composed by John Williams, the film's opening and end title music was lifted excerpts from Im Zeichen des Bösen (1958), which was scored by Henry Mancini.
Virginia Christine, who plays the blind secretary at the Sage Home for the Blind, was also in Rächer der Unterwelt (1946), of which this film is a remake.